Diflomotecan is an E-ring modified camptothecin analogue, which possesses greater lactone stability in plasma compared with other topoisomerase I inhibitors. Diflomotecan is also a 10,11-difluoro-homocamptothecin, represents a new promising class of topoisomerase I inhibitors with enhanced plasma stability and superior preclinical anti-tumour activity as compared to the established camptothecins, irinotecan and topotecan. Diflomotecan was the first homocamptothecin to enter clinical studies. Phase I data are summarized for both the intravenous and oral schedules. The toxicity is primarily haematological while no severe gastrointestinal toxicity has been observed in contrast to other topoisomerase I inhibitors. Diflomotecan has a high oral bioavailability (72 - 95%) and the oral day 1 - 5 every 3 weeks regimen is recommended for Phase II testing because it is relatively well tolerated, convenient and mimics protracted exposure.

Diflomotecan, a 10,11-difluoro-homocamptothecin, represents a new promising class of topoisomerase I inhibitors with enhanced plasma stability and superior preclinical anti-tumour activity as compared to the established camptothecins, irinotecan and topotecan. Diflomotecan was the first homocamptothecin to enter clinical studies. Phase I data are summarized for both the intravenous and oral schedules. The toxicity is primarily haematological while no severe gastrointestinal toxicity has been observed in contrast to other topoisomerase I inhibitors. Diflomotecan has a high oral bioavailability (72 - 95%) and the oral day 1 - 5 every 3 weeks regimen is recommended for Phase II testing because it is relatively well tolerated, convenient and mimics protracted exposure. This review summarizes the developments and innovations in the topoisomerase I inhibitor field with an emphasis on diflomotecan.

2.A multicentre phase I and pharmacokinetic study of BN80915 (diflomotecan) administered daily as a 20-min intravenous infusion for 5 days every 3 weeks to patients with advanced solid tumours.

BACKGROUND: BN80915 (diflomotecan) is an E-ring modified camptothecin analogue, which possesses greater lactone stability in plasma compared with other topoisomerase I inhibitors. This phase I study was carried out using a daily times five administration schedule (dx5) repeated three weekly. The primary objective was to determine the maximum tolerated dose (MTD) and recommended dose (RD) for phase II studies. Secondary objectives were to determine the safety and pharmacokinetic (PK) profile, and to make a preliminary assessment of antitumour activity.

Two practical, efficient, and scalable asymmetric routes to DE ring fragment 7, a key building block in the synthesis of the homocamptothecin derivative diflomotecan 4, are described. The "acetal route" starts from 2-chloro-4-cyanopyridine 8 and represents an enantioselective and optimized modification of the original racemic discovery chemistry synthesis. The inefficient optical resolution procedure was replaced by an efficient asymmetric acetate aldol addition (dr 87:13) to a ketone substrate as the key step generating the (R)-configured quaternary stereocenter with high stereoselectivity. 7 was finally obtained in 8.9% overall yield (er 99.95:0.05) over nine steps, avoiding chromatographic purifications and comparing favorably with the initial procedure. In the related "amide route" starting from 2-chloroisonicotinic acid 41, a secondary amide directing group was used to facilitate the ortho lithiation of the pyridine 3-position. The key step of this protocol again consists of a practical asymmetric acetate aldol addition (dr = 87:13).

4.Reduced expression of DNA topoisomerase I in SF295 human glioblastoma cells selected for resistance to homocamptothecin and diflomotecan.

Homocamptothecins (hCPTs) are a novel class of topoisomerase I (Top1) inhibitors with enhanced chemical stability compared with the currently used camptothecin (CPT) analogs irinotecan and topotecan. The hCPT derivative diflomotecan (BN80915) is currently in clinical trials. We established two resistant human glioblastoma cell lines, SF295/hCPT50 and SF295/BN50, by stepwise exposure of the parental SF295 line to increasing concentrations of hCPT and BN80915, respectively. The two resistant cell lines were 15- to 22-fold resistant to hCPT and BN80915 as well as 7- to 27-fold cross-resistant to other Top1 inhibitors, including CPT, topotecan, and the indenoisoquinolines MJ-III-65 (NSC 706744) and NSC 724998, but sensitive to the topoisomerase II inhibitors mitoxantrone and etoposide. Neither of the resistant cell lines displayed any detectable expression of the three major drug transporters P-glycoprotien, multidrug resistance-associated protein 1, or ATP-binding cassette, subfamily G (WHITE), member 2, as assessed by immunoblot or flow cytometry.